1. Field of the Invention
The present invention relates to ultrasonic transducers, and in particular to ultrasonic transducers suitable for use as immersion-type ultrasonic transducers used in quality control and flaw detector applications.
2. Description of the Related Art
Immersion-type ultrasonic transducers which are suitable for use in quality control and flaw detection applications are generally known in the art. One type of known ultrasonic transducer used in this service employs a single ceramic piezoelectric element contained in a housing, with the ceramic piezoelectric element being used to both transmit acoustic energy and to detect the reflected acoustic energy from the object undergoing evaluation. However, most piezoelectric materials heretofore used in these immersion-type ultrasonic transducers, including the aforenoted piezoelectric ceramic materials, are limited in their performance due to impedance mismatches between the transducer and the immersion medium, which is water in most cases. Further, while piezoelectric ceramics are generally regarded as having good acoustic energy transmissive properties, in converting electric energy pulses into sound energy, the piezoelectric ceramics perform relatively poorly in a receiving capacity, wherein sound wave pressures must be converted into a voltage by the material.
Polymeric piezoelectric materials are known to have a better impedance match with water than, for example, the ceramic piezoelectric materials, however the polymeric piezoelectrics are poor transmitters of acoustic energy. Polymeric piezoelectric materials do, however, work well as receivers or detectors of acoustic energy. Because of the poor transmission characteristics, the polymeric piezoelectric materials have seen only limited use in ultrasonic transducers. Principally, such materials have been used as dedicated receiver elements in systems which employ separate transmitter and receiver elements. The use of separate elements, however, results in a decrease in the accuracy of and/or an increase in the complexity of pinpointing the location of flaws in the item being inspected.
It is a principal object of the present invention to provide an ultrasonic transducer which includes within a single housing both a transmitter element having good acoustic energy transmitting properties and a receiver element having good acoustic energy receiving characteristics as well as an improved impedance match with an immersion medium.
It is another principal object of the present invention to provide an ultrasonic transducer which, within a single housing, takes advantage of the transmission properties of a ceramic piezoelectric, and which also takes advantage of the improved receiving properties and closer impedance match of the polymeric piezoelectric, thus eliminating or substantially reducing the problems heretofore associated with the less-than-desirable properties of each of these two material when used in ultrasonic transducers.
It is a further object of the present invention to employ both a ceramic piezoelectric material layer and a polymeric piezoelectric material layer as a transmitter means and a receiver means, respectively, in a transducer assembly which is packaged to have an external configuration which is substantially identical to a standard, known immersion-type transducer.